refactor: Event sourcing 2445 (#2518)

* #2445 Refactored event sourcing

* #2445 Minor cleanup

* #2445 Formatted with Google java style guide

* #2445 Fixed Javadoc

* #2445 Fixing sonar gate bug

event-sourcing/pom.xml

@@ -40,8 +40,8 @@
       <scope>test</scope>
     </dependency>
     <dependency>
-      <groupId>com.google.code.gson</groupId>
-      <artifactId>gson</artifactId>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-databind</artifactId>
     </dependency>
   </dependencies>
   <build>

event-sourcing/src/main/java/com/iluwatar/event/sourcing/app/App.java

@@ -28,6 +28,7 @@ import com.iluwatar.event.sourcing.event.AccountCreateEvent;
 import com.iluwatar.event.sourcing.event.MoneyDepositEvent;
 import com.iluwatar.event.sourcing.event.MoneyTransferEvent;
 import com.iluwatar.event.sourcing.processor.DomainEventProcessor;
+import com.iluwatar.event.sourcing.processor.JsonFileJournal;
 import com.iluwatar.event.sourcing.state.AccountAggregate;
 import java.math.BigDecimal;
 import java.util.Date;
@@ -42,16 +43,18 @@ import lombok.extern.slf4j.Slf4j;
  * transactional data, and maintain full audit trails and history that can enable compensating
  * actions.
  *
- * <p>This App class is an example usage of an Event Sourcing pattern. As an example, two bank accounts
- * are created, then some money deposit and transfer actions are taken, so a new state of accounts is
- * created. At that point, state is cleared in order to represent a system shut-down. After the shut-down,
- * system state is recovered by re-creating the past events from event journals. Then state is
- * printed so a user can view the last state is same with the state before a system shut-down.
+ * <p>This App class is an example usage of an Event Sourcing pattern. As an example, two bank
+ * accounts are created, then some money deposit and transfer actions are taken, so a new state of
+ * accounts is created. At that point, state is cleared in order to represent a system shut-down.
+ * After the shut-down, system state is recovered by re-creating the past events from event
+ * journals. Then state is printed so a user can view the last state is same with the state before a
+ * system shut-down.
  *
  * <p>Created by Serdar Hamzaogullari on 06.08.2017.
  */
 @Slf4j
 public class App {
+
   /**
    * The constant ACCOUNT OF DAENERYS.
    */
@@ -68,8 +71,7 @@ public class App {
    */
   public static void main(String[] args) {
 
-    var eventProcessor = new DomainEventProcessor();
-
+    var eventProcessor = new DomainEventProcessor(new JsonFileJournal());
 
     LOGGER.info("Running the system first time............");
     eventProcessor.reset();
@@ -103,7 +105,7 @@ public class App {
 
     LOGGER.info("Recover the system by the events in journal file............");
 
-    eventProcessor = new DomainEventProcessor();
+    eventProcessor = new DomainEventProcessor(new JsonFileJournal());
     eventProcessor.recover();
 
     LOGGER.info("...............Recovered State:............");

event-sourcing/src/main/java/com/iluwatar/event/sourcing/event/AccountCreateEvent.java

@@ -24,14 +24,15 @@
  */
 package com.iluwatar.event.sourcing.event;
 
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
 import com.iluwatar.event.sourcing.domain.Account;
 import com.iluwatar.event.sourcing.state.AccountAggregate;
 import lombok.Getter;
 
 /**
- * This is the class that implements account created event.
- * Holds the necessary info for an account created event.
- * Implements the process function that finds the event-related domain objects and
+ * This is the class that implements account created event. Holds the necessary info for an account
+ * created event. Implements the process function that finds the event-related domain objects and
  * calls the related domain object's handle event functions
  *
  * <p>Created by Serdar Hamzaogullari on 06.08.2017.
@@ -50,7 +51,10 @@ public class AccountCreateEvent extends DomainEvent {
    * @param accountNo   the account no
    * @param owner       the owner
    */
-  public AccountCreateEvent(long sequenceId, long createdTime, int accountNo, String owner) {
+  @JsonCreator
+  public AccountCreateEvent(@JsonProperty("sequenceId") long sequenceId,
+      @JsonProperty("createdTime") long createdTime,
+      @JsonProperty("accountNo") int accountNo, @JsonProperty("owner") String owner) {
     super(sequenceId, createdTime, "AccountCreateEvent");
     this.accountNo = accountNo;
     this.owner = owner;

event-sourcing/src/main/java/com/iluwatar/event/sourcing/event/MoneyDepositEvent.java

@@ -24,6 +24,8 @@
  */
 package com.iluwatar.event.sourcing.event;
 
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
 import com.iluwatar.event.sourcing.state.AccountAggregate;
 import java.math.BigDecimal;
 import java.util.Optional;
@@ -50,7 +52,10 @@ public class MoneyDepositEvent extends DomainEvent {
    * @param accountNo   the account no
    * @param money       the money
    */
-  public MoneyDepositEvent(long sequenceId, long createdTime, int accountNo, BigDecimal money) {
+  @JsonCreator
+  public MoneyDepositEvent(@JsonProperty("sequenceId") long sequenceId,
+      @JsonProperty("createdTime") long createdTime,
+      @JsonProperty("accountNo") int accountNo, @JsonProperty("money") BigDecimal money) {
     super(sequenceId, createdTime, "MoneyDepositEvent");
     this.money = money;
     this.accountNo = accountNo;

event-sourcing/src/main/java/com/iluwatar/event/sourcing/event/MoneyTransferEvent.java

@@ -24,6 +24,8 @@
  */
 package com.iluwatar.event.sourcing.event;
 
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
 import com.iluwatar.event.sourcing.state.AccountAggregate;
 import java.math.BigDecimal;
 import java.util.Optional;
@@ -52,8 +54,11 @@ public class MoneyTransferEvent extends DomainEvent {
    * @param accountNoFrom the account no from
    * @param accountNoTo   the account no to
    */
-  public MoneyTransferEvent(long sequenceId, long createdTime, BigDecimal money, int accountNoFrom,
-                            int accountNoTo) {
+  @JsonCreator
+  public MoneyTransferEvent(@JsonProperty("sequenceId") long sequenceId,
+      @JsonProperty("createdTime") long createdTime,
+      @JsonProperty("money") BigDecimal money, @JsonProperty("accountNoFrom") int accountNoFrom,
+      @JsonProperty("accountNoTo") int accountNoTo) {
     super(sequenceId, createdTime, "MoneyTransferEvent");
     this.money = money;
     this.accountNoFrom = accountNoFrom;

event-sourcing/src/main/java/com/iluwatar/event/sourcing/processor/DomainEventProcessor.java

@@ -28,13 +28,17 @@ import com.iluwatar.event.sourcing.event.DomainEvent;
 
 /**
  * This is the implementation of event processor. All events are processed by this class. This
- * processor uses processorJournal to persist and recover events.
+ * processor uses eventJournal to persist and recover events.
  *
  * <p>Created by Serdar Hamzaogullari on 06.08.2017.
  */
 public class DomainEventProcessor {
 
-  private final JsonFileJournal processorJournal = new JsonFileJournal();
+  private final EventJournal eventJournal;
+
+  public DomainEventProcessor(EventJournal eventJournal) {
+    this.eventJournal = eventJournal;
+  }
 
   /**
    * Process.
@@ -43,14 +47,14 @@ public class DomainEventProcessor {
    */
   public void process(DomainEvent domainEvent) {
     domainEvent.process();
-    processorJournal.write(domainEvent);
+    eventJournal.write(domainEvent);
   }
 
   /**
    * Reset.
    */
   public void reset() {
-    processorJournal.reset();
+    eventJournal.reset();
   }
 
   /**
@@ -58,7 +62,7 @@ public class DomainEventProcessor {
    */
   public void recover() {
     DomainEvent domainEvent;
-    while ((domainEvent = processorJournal.readNext()) != null) {
+    while ((domainEvent = eventJournal.readNext()) != null) {
       domainEvent.process();
     }
   }

event-sourcing/src/main/java/com/iluwatar/event/sourcing/processor/EventJournal.java

@@ -0,0 +1,37 @@
+package com.iluwatar.event.sourcing.processor;
+
+import com.iluwatar.event.sourcing.event.DomainEvent;
+import java.io.File;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * Base class for Journaling implementations.
+ */
+@Slf4j
+public abstract class EventJournal {
+
+  File file;
+
+  /**
+   * Write.
+   *
+   * @param domainEvent the domain event.
+   */
+  abstract void write(DomainEvent domainEvent);
+
+  /**
+   * Reset.
+   */
+  void reset() {
+    if (file.delete()) {
+      LOGGER.info("File cleared successfully............");
+    }
+  }
+
+  /**
+   * Read domain event.
+   *
+   * @return the domain event.
+   */
+  abstract DomainEvent readNext();
+}

event-sourcing/src/main/java/com/iluwatar/event/sourcing/processor/JsonFileJournal.java

@@ -24,9 +24,8 @@
  */
 package com.iluwatar.event.sourcing.processor;
 
-import com.google.gson.Gson;
-import com.google.gson.JsonElement;
-import com.google.gson.JsonParser;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import com.iluwatar.event.sourcing.event.AccountCreateEvent;
 import com.iluwatar.event.sourcing.event.DomainEvent;
 import com.iluwatar.event.sourcing.event.MoneyDepositEvent;
@@ -49,9 +48,8 @@ import java.util.List;
  *
  * <p>Created by Serdar Hamzaogullari on 06.08.2017.
  */
-public class JsonFileJournal {
+public class JsonFileJournal extends EventJournal {
 
-  private final File file;
   private final List<String> events = new ArrayList<>();
   private int index = 0;
 
@@ -81,22 +79,12 @@ public class JsonFileJournal {
    *
    * @param domainEvent the domain event
    */
+  @Override
   public void write(DomainEvent domainEvent) {
-    var gson = new Gson();
-    JsonElement jsonElement;
-    if (domainEvent instanceof AccountCreateEvent) {
-      jsonElement = gson.toJsonTree(domainEvent, AccountCreateEvent.class);
-    } else if (domainEvent instanceof MoneyDepositEvent) {
-      jsonElement = gson.toJsonTree(domainEvent, MoneyDepositEvent.class);
-    } else if (domainEvent instanceof MoneyTransferEvent) {
-      jsonElement = gson.toJsonTree(domainEvent, MoneyTransferEvent.class);
-    } else {
-      throw new RuntimeException("Journal Event not recognized");
-    }
-
+    var mapper = new ObjectMapper();
     try (var output = new BufferedWriter(
         new OutputStreamWriter(new FileOutputStream(file, true), StandardCharsets.UTF_8))) {
-      var eventString = jsonElement.toString();
+      var eventString = mapper.writeValueAsString(domainEvent);
       output.write(eventString + "\r\n");
     } catch (IOException e) {
       throw new RuntimeException(e);
@@ -104,14 +92,6 @@ public class JsonFileJournal {
   }
 
 
-  /**
-   * Reset.
-   */
-  public void reset() {
-    file.delete();
-  }
-
-
   /**
    * Read the next domain event.
    *
@@ -124,19 +104,19 @@ public class JsonFileJournal {
     var event = events.get(index);
     index++;
 
-    var parser = new JsonParser();
-    var jsonElement = parser.parse(event);
-    var eventClassName = jsonElement.getAsJsonObject().get("eventClassName").getAsString();
-    var gson = new Gson();
+    var mapper = new ObjectMapper();
     DomainEvent domainEvent;
-    if (eventClassName.equals("AccountCreateEvent")) {
-      domainEvent = gson.fromJson(jsonElement, AccountCreateEvent.class);
-    } else if (eventClassName.equals("MoneyDepositEvent")) {
-      domainEvent = gson.fromJson(jsonElement, MoneyDepositEvent.class);
-    } else if (eventClassName.equals("MoneyTransferEvent")) {
-      domainEvent = gson.fromJson(jsonElement, MoneyTransferEvent.class);
-    } else {
-      throw new RuntimeException("Journal Event not recegnized");
+    try {
+      var jsonElement = mapper.readTree(event);
+      var eventClassName = jsonElement.get("eventClassName").asText();
+      domainEvent = switch (eventClassName) {
+        case "AccountCreateEvent" -> mapper.treeToValue(jsonElement, AccountCreateEvent.class);
+        case "MoneyDepositEvent" -> mapper.treeToValue(jsonElement, MoneyDepositEvent.class);
+        case "MoneyTransferEvent" -> mapper.treeToValue(jsonElement, MoneyTransferEvent.class);
+        default -> throw new RuntimeException("Journal Event not recognized");
+      };
+    } catch (JsonProcessingException jsonProcessingException) {
+      throw new RuntimeException("Failed to convert JSON");
     }
 
     domainEvent.setRealTime(false);

event-sourcing/src/test/java/IntegrationTest.java

@@ -22,6 +22,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+
 import static com.iluwatar.event.sourcing.app.App.ACCOUNT_OF_DAENERYS;
 import static com.iluwatar.event.sourcing.app.App.ACCOUNT_OF_JON;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -30,6 +31,7 @@ import com.iluwatar.event.sourcing.event.AccountCreateEvent;
 import com.iluwatar.event.sourcing.event.MoneyDepositEvent;
 import com.iluwatar.event.sourcing.event.MoneyTransferEvent;
 import com.iluwatar.event.sourcing.processor.DomainEventProcessor;
+import com.iluwatar.event.sourcing.processor.JsonFileJournal;
 import com.iluwatar.event.sourcing.state.AccountAggregate;
 import java.math.BigDecimal;
 import java.util.Date;
@@ -53,7 +55,7 @@ class IntegrationTest {
    */
   @BeforeEach
   void initialize() {
-    eventProcessor = new DomainEventProcessor();
+    eventProcessor = new DomainEventProcessor(new JsonFileJournal());
   }
 
   /**
@@ -84,7 +86,7 @@ class IntegrationTest {
 
     AccountAggregate.resetState();
 
-    eventProcessor = new DomainEventProcessor();
+    eventProcessor = new DomainEventProcessor(new JsonFileJournal());
     eventProcessor.recover();
 
     var accountOfDaenerysAfterShotDown = AccountAggregate.getAccount(ACCOUNT_OF_DAENERYS);